fix an issue where SensorService could request an invalid sensor delay

When the app requests "fastest", the java layer encodes this as a
delay of 0. SensorService was passing this unchanged to the HAL.
However the HAL is required to reject delays lower that the
advertised lower delay.

Change-Id: I92be77acd3af62ffeb49e4b31e24ddcd203510e2

Author: pixelflinger

services/sensorservice/SensorService.cpp

@@ -471,14 +471,20 @@ status_t SensorService::setEventRate(const sp<SensorEventConnection>& connection
     if (mInitCheck != NO_ERROR)
         return mInitCheck;
 
+    SensorInterface* sensor = mSensorMap.valueFor(handle);
+    if (!sensor)
+        return BAD_VALUE;
+
     if (ns < 0)
         return BAD_VALUE;
 
+    if (ns == 0) {
+        ns = sensor->getSensor().getMinDelayNs();
+    }
+
     if (ns < MINIMUM_EVENTS_PERIOD)
         ns = MINIMUM_EVENTS_PERIOD;
 
-    SensorInterface* sensor = mSensorMap.valueFor(handle);
-    if (!sensor) return BAD_VALUE;
     return sensor->setDelay(connection.get(), handle, ns);
 }